WO2003022544A2

WO2003022544A2 - Continuous heat treatment of bulk material

Info

Publication number: WO2003022544A2
Application number: PCT/CH2002/000442
Authority: WO
Inventors: Christian Dachauer; Camille Borer; Hans Geissbühler
Original assignee: Bühler AG
Priority date: 2001-09-11
Filing date: 2002-08-13
Publication date: 2003-03-20
Also published as: WO2003022544A3; BR0212059A; ATE482065T1; US7350318B2; DE10144747A1; EP1425146B1; MXPA04001702A; CN1549762A; US20040229182A1; EA005330B1; EP1425146A2; DE50214675D1; CN1549762B; ES2353205T3; BR0212059B1; KR20040062537A; PL367720A1; JP2005500928A; EA200400424A1

Abstract

The invention relates to a device (1) for continuous heat treatment of granulated materials, especially to the crystallization of polymer granulate, such as polyethylenterephthalate (PET) for example. The device comprises several adjacent fluidization chambers (2, 3, 4, 5, 6) respectively provided with a sieve plate (11) through which a fluidization gas used to fluidize the granulate can be insufflated into the respective chamber from below via a gas inlet (9), said gas being able to escape via a gas outlet (10) in the top area of the device. The first chamber (2) takes up the greater part of the overall volume of all chambers (2, 3, 4, 5, 6) and neighbouring chambers are, respectively, fluidically connected by means of product throughflow openings (18, 19, 20, 21; 28, 29, 30, 31) in the separating walls (14, 15, 16, 17) arranged therebetween. According to the inventive method, using the inventive device (1), the granulated material is guided through several adjacent fluidization chambers (2, 3, 4, 5, 6), the absolute filling level of the fluidized granulating material in the first chamber (2) being at least as high as the absolute filling level of the other adjacent chambers (3, 4, 5, 6) disposed downstream therefrom.

Description

Continuous thermal treatment of bulk goods

The invention relates to a device for the continuous thermal treatment of granular bulk materials, in particular for crystallizing polymer granules, such as e.g. Polyethylene terephthalate (PET), with a product inlet that opens into a first most upstream chamber and a product outlet that connects to a most downstream chamber. The invention also relates to a method for the continuous thermal treatment of a granular bulk material, in particular for crystallizing polymer granules, such as e.g. Polyethylene terephthalate (PET), using the device according to the invention.

Such a device is e.g. known from EP 0 712 703 A2. It consists of a housing with an input and an output for thermally treated plastic flakes (chips). The interior of the housing is divided by a plurality of partitions into a first large chamber and a number of smaller chambers, the partition between the first chamber and the chambers adjoining it being higher than the partitions between the respective smaller chambers. All chambers can be gassed from below via a sieve tray in order to fluidize the flaky product. In operation, the fluidized product flows from chamber to chamber over the upper edge of the respective partition. Unwanted backmixing can occur due to the bubbling movement in the respective fluidization chambers, in that flakes spring back from a chamber or are blown back into the chamber located upstream from it. This then results in different residence time spectra for different flakes, which inevitably leads to flakes with different product quality.

DE 195 00 383 A1 discloses a device for the continuous crystallization of polyester material in granular form. The thermal treatment takes place in a cylindrical treatment room, which is also gassed from below through a sieve tray in order to fluidize the granulate with the treatment gas. The Ver- Turning only one treatment room, in which the fluidization takes place, saves costs and makes the use of stirring tools and the like superfluous, but here too a very narrow residence time spectrum of the particles and thus a largely uniform product quality of the granules cannot yet be achieved.

EP 0 379 684 A2 discloses an apparatus and a method for the continuous crystallization of polyester material in granular form. The device consists of two separately arranged fluidization chambers (fluidized bed apparatuses), the first chamber being a bubbling fluidized bed with a mixing characteristic and the second chamber being a fluidized bed with a piston flow characteristic. This combination of two different fluidization chambers achieves a surprisingly homogeneous product quality, but each of the two separate fluidized bed apparatuses requires its own circuit with channels, fans, heat exchangers for the gassing and fluidizing gas, and cyclone separators or filters for separating dust that is caused by abrasion from the granulate particles.

The present invention is therefore based on the object of providing an inexpensive and easy-to-operate device and a method of the type mentioned at the beginning, in which or in which a narrow residence time spectrum of the fluidized and thermally treated granulate particles in the device and thus a homogeneous product quality is achieved ,

This object is achieved according to the invention in the device described in the introduction in that the device has a plurality of adjoining fluidization chambers, each with a sieve bottom, through which a fluidization gas for fluidizing the granules can be blown into the respective chamber, which escape via a gas outlet in the ceiling area of the device can, wherein the first chamber occupies a large part of the total volume of all chambers, and that adjacent chambers each have a fluid connection via product passages in the partition walls arranged between them.

This simple, compact design is particularly material and space-saving. Due to the adjoining chambers, heat loss or the required The need for heat insulation is significantly reduced and ultimately energy-saving operation is made possible. In addition, as the number of chambers increases, the residence time spectrum for granules in the device becomes ever narrower. The fact that no intermediate conveyance over a distance between the chambers is necessary is also particularly advantageous. In addition, it is sufficient to work with only one gassing / fluidization stream introduced over the entire sieve plate. Overall, the device according to the invention can therefore be provided inexpensively, and the method according to the invention and the maintenance of the device according to the invention also prove to be inexpensive.

Product passages between adjacent chambers are preferably arranged on the bottom side between the sieve bottom and a lower end region of the dividing wall between the adjacent chambers. Alternatively or additionally, the product passages can also be arranged between adjacent chambers on the wall side between a side wall and a lateral end region of the partition between the adjacent chambers. Surprisingly, with this arrangement of the product passages, little backmixing occurs between the chambers. In addition, this arrangement facilitates emptying of the device after operation e.g. for cleaning or maintenance purposes or when changing products.

Product passages are also expediently arranged in the partition approximately at the height of the upper end of the fluidized bed.

In a particularly advantageous embodiment, the product passages extend over the entire width or over the entire height of the device from one side wall to the other side wall or from the sieve bottom to the upper end of the fluidized bed, the product passages preferably being designed as horizontal or vertical slots. In particular, the slit-like product passages each extend along the entire width or along the entire height of a partition. Preferably, only horizontal slots are used as product passages in order to achieve a narrow residence time spectrum. In a further particularly advantageous embodiment, the product passages are arranged alternately on the floor and at the level of the upper end of the fluidized bed on dividing walls which follow one another along the product conveying direction. In this way, all particles of the product are forced through the device in a roller coaster-like manner, and for each chamber the product inlet is as far as possible from the product outlet, so that all particles have to travel a relatively long way through the respective chamber. If, on the other hand, the product passages were on the floor in the case of successive partition walls, a particle could, under certain circumstances, migrate directly from product passage to product passage through this chamber without being in this chamber for longer. This would be counterproductive for the narrow residence time spectrum aimed for in the device. Alternatively, the product passages can also be arranged alternately on the left-hand end of the wall and on the right-hand end of the dividing wall on partitions that follow one another along the product conveying direction. Analogously, the particles are forced here on a slalom-like path within the device. Both the roller coaster configuration and the slalom configuration have a positive effect on the homogenization of the product residence times and thus additionally contribute to the multi-chambered nature of the device for a narrow residence time spectrum.

It is also expedient if the position of the product passages is adjustable. This allows product-specific optimizations to be carried out, e.g. an adjustment of the average residence time of the granules in the device.

In this context, it is also particularly advantageous if the cross-sectional extent of the product passages is adjustable. This enables optimization by adapting to the respective grain size of the granulate.

A minimum dimension, in particular the slot width of the cross-sectional dimension of the product passages, is preferably set such that it lies in the range between a minimum granule dimension and approximately 20 cm. A particularly preferred minimum dimension, in particular the slot width of the cross-sectional dimension of the product passages, is in the range between twice the minimum granule dimension and approximately 10 times the minimum granule dimension. Also this helps to make a direct flow through a chamber for a granulate particle from the entrance into the chamber to the exit from the chamber less likely. Thus, at least short dwell times are made practically impossible. This is particularly advantageous and useful for the crystallization of polyesters such as PET, since a too short dwell time of a polyester pellet leads to inadequate crystallization, which results in pellets that tend to stick. On the other hand, a somewhat excessive dwell time does not have a negative effect on product homogeneity in the crystallization of polyester, since the time-dependent increase in the degree of crystallization initially increases steeply and then quickly changes into a saturation range. Another advantage is that the likelihood of backmixing is also minimal, which additionally increases the thermal efficiency of the device and keeps each chamber at a defined temperature.

Another preferred embodiment is characterized in that the bottom or the product passages arranged approximately at the level of the upper end of the fluidized bed in the partition or the wall-side product passages are each essentially parallel to the bottom or the respective side wall and essentially perpendicular to the partition have arranged sheet metal, which is attached to the edge of the respective product passage and extends through the product passage on both sides of this partition in each case into the two adjacent chambers. In this way, a product passage is created, which is designed as a kind of tunnel between this sheet and the floor or the side wall. A particle that gets into this tunnel against the predominant flow of the fluidized product is therefore likely to be reflected back and forth between the tunnel walls and thus has a longer dwell time in the product passage, which greatly increases the likelihood that sooner or later it will be caused by impacts entrained with other particles of the fluidized product stream. This version of the tunnel also makes backmixing with the negative consequences mentioned more difficult and ultimately makes it practically impossible.

Advantageously, in the area of the product passages at the bottom and essentially opposite the sheet metal, there are blow-in areas in the sieve tray which allow fluidizing gas to be blown into the chamber at a speed. which enables both a speed component perpendicular to the blowing area and a speed component parallel to the blowing area in the direction of the fluidized granulate flow. For this purpose, so-called Konidur sheet metal is preferably used, in which the openings of the sieve bottom are not formed by completely punching out and removing material, but rather are formed by only partially punching out and then bending over the partially punched-out material part. Thus, in the area of the product passage and in particular in the tunnel version in the area of the tunnel, in addition to the fluidization component directed vertically upward, a horizontal transport component can be transferred to the product, which also makes backmixing more difficult.

If necessary, it is also possible to connect at least the first chamber via its sieve plate to an associated feed channel for fluidizing gas, which is separated from a common feed channel for the remaining chambers. This can e.g. can be achieved by a common air circuit which has a branch in front of the sieve plate of the first chamber and the common sieve plate of the remaining chambers, an adjustable flap being provided in each branch serving as a feed line to the respective sieve plate and as a discharge line from the respective chambers of the device , by means of which the gas distribution and thus also the gas velocity for the fluidization of the respective chambers can be adjusted. This enables the first chamber to be gassed and fluidized under different conditions than the remaining chambers. For example, during the crystallization of polyester in the first chamber with a higher gas velocity through the sieve bottom than in the remaining chambers. The advantage then lies in the fact that in the case of the product which has not yet crystallized or has hardly crystallized in the first chamber and which tends to stick much more than the product which is already in the subsequent remaining chambers, the higher gas velocity means greater fluidization and thus more Prevention of agglomerate formation is effected.

In most cases, however, it is sufficient if all of the chambers are assigned to a common supply channel for fluidizing gas via their respective sieve plates are. This saves material costs on the device and simplifies operation.

Preferably, an impact resolver is provided at the product outlet, into which the product outlet opens. This impact resolver finally dissolves agglomerates that have formed despite all the other precautions.

The sieve trays of all chambers can be arranged on one level. Alternatively, the device can consist of chambers lined up along the fluidized granulate stream with mutually offset heights.

The first chamber is preferably defined in its floor plan by a wall which surrounds it cylindrically, and the remaining chambers are concentrically connected radially outward around the first chamber with cylindrical walls. This design is particularly space and material saving, and the heat losses are also low. Alternatively, the first chamber can be defined by a pair of concentric cylindrical walls, the remaining chambers within the inner cylindrical wall of the first chamber adjoining radially inward concentrically with cylindrical walls.

Instead of the cylindrical plan, the plan of the first chamber can also be rectangular and the remaining chambers adjoin the outside of the first chamber. In addition to the advantages already mentioned with the cylindrical geometry, there is also the fact that the rectangular shape is particularly easy to build. Alternatively, the first chamber can also be rectangular in shape here, with the remaining chambers inside the first chamber e.g. connect nested with each other with a rectangular plan concentrically.

In all the embodiments mentioned so far, it is particularly advantageous if at least the remaining chambers are each designed in such a way that the ratio between the layer height of the fluidized granules and the smallest floor plan chamber dimension is in the range from 0.5 to 2. This preferred benchmark for that This ratio ensures that no excessive blistering can take place inside the fluidized product. If the layer height of the fluidized product is much greater than twice the smallest floor plan chamber dimension, many small bubbles can form a few or even one large bubble during the ascent, which due to the decreasing gravitational pressure in the fluidized Move the product upwards and then create impacts when reaching the fluidized bed surface and / or cause the granulate particles to be thrown around. On the other hand, if the floor is only thinly covered with product, economical fluidization is not possible.

The most upstream first chamber preferably takes up a large part of the total volume of all chambers, in particular approximately half of the total volume of all chambers. The sieve bottom surface of the first chamber expediently also takes up a large part of the total sieve bottom surface of all the chambers, again about half of the total sieve bottom surface of all chambers. This is particularly advantageous in the crystallization of polyester. As a result, extensive crystallization can be achieved in the first chamber in a first crystallization step for the majority of all particles. Since individual particles are still sticky in this first phase, it is particularly important to generate large-volume fluidization with a lower particle density in the first chamber than in the subsequent remaining chambers. Then the likelihood of two sticky particles hitting each other and thus agglomerate formation is much less.

At the downstream end of the last chamber, the product outlet in a wall is expediently designed like a window with a slide, by means of which the lower edge of the window can be adjusted. Alternatively, at the downstream end of the last chamber, the product outlet can be designed as a kind of pivotable weir, the height of which can be adjusted by pivoting the weir.

In order to prevent that, together with the fluidizing gas drawn off in the ceiling area of the device, individual granulate particles escape from the device, for example if larger bubbles reach the fluidized bed surface, is above the A so-called zigzag separator is arranged in front of the fluidized bed, which allows gas to pass through and holds up granulate particles and directs them back into the fluidized bed.

According to the invention, the granules are passed through the several fluidizing chambers arranged in a row, each having a sieve plate through which a fluidizing gas (for example pure nitrogen or air) is blown into the respective chamber from below to fluidize the granules and is drawn off in the ceiling area of the device, the absolute filling level of the fluidized granules in the first chamber is at least as high as the absolute filling level of the remaining chambers downstream.

Expediently, fluidization gas is blown into all chambers with a uniform first treatment temperature, the fluidization gas preferably also being used as a heat source for heating the fluidized granulate. This uniform first treatment temperature is in the case of crystallization of PET about 180 ^C C. The still predominantly amorphous starting material occurs in the form of pellets with a temperature of about 20 ° C and at this low temperature non-adhesive in the first chamber. In the first chamber there is still no complete heat transfer to the PET granulate, which in turn is advantageous since the tendency to stick when heated is still very strong in the amorphous or only slightly crystallized state. A further rise in the temperature of the PET granules takes place in the adjoining chambers, since in these chambers the initial temperature is already higher than in the previous chamber and gas of the same treatment temperature is blown into each chamber. This means that an optimal crystallization process for PET can be set, in which the temperature of the PET granulate increases from chamber to chamber in the direction of the optimal crystallization temperature, while at the same time the degree of crystallization of the PET increases from chamber to chamber, thus keeping the tendency to stick even at increasing temperatures becomes.

If necessary, the fluidizing gas can at least partially contain a gas reacting with the fluidized granulate. This can be a disinfectant or flavoring gas, for example when drying food. A fluidizing gas with a second treatment temperature is expediently blown into at least one of the remaining chambers and is preferably used as a heat sink for cooling the fluidized granules.

Fluidizing gas is preferably blown into all chambers with the same excess pressure and the same gas velocity. If necessary, however, fluidizing gas can be blown into the first chamber at a higher pressure and / or higher gas velocity than in the remaining chambers. The higher gas velocity leads to greater fluidization, i.e. Expansion of the fluidized bed, while the higher gas pressure enables more heat to be supplied via the fluidizing gas.

Further advantages, features and possible applications result from the following description of a preferred embodiment with reference to the drawing, in which:

Fig. 1 is a sectional view along a vertical plane of a first

Embodiment of the invention is;

Fig. 2 is a sectional view along a vertical plane of a second

Embodiment of the invention is;

3a and 3b are a sectional view along a vertical plane and a

Fig. 4 is a sectional view along a horizontal plane of a third embodiment of the invention;

4 is a diagram showing the dependence of the residence time spectrum of granulate particles in the device according to the invention as a function of the number of chambers of the device;

5a and 5b schematically show a one-stage fluidized bed and a 5-stage fluidized bed, respectively; 5c shows the local temperature profile of the product of the fluidized bed from FIG. 5a or the fluidized bed from FIG. 5b;

6a shows a first special embodiment of the product passages between the chambers; and

6b shows a second special embodiment of the product passages between the chambers in an enlarged view.

1 schematically shows a vertical sectional view of a first exemplary embodiment of the device 1 according to the invention. The device 1 according to the invention forms a multi-box crystallizer with a housing 13, in the interior of which several chambers 2, 3, 4, 5 and 6 are separated from one another by partition walls 14, 15, 16 and 17 are separated. The bottom of the chambers is formed by a sieve bottom 11 through which a fluidizing gas can be blown in from below. The chambers are delimited at the top by a zigzag separator 12, which forms the chamber ceiling. The front and rear boundaries of the chambers 2, 3, 4, 5 and 6 run parallel above and below the plane of the drawing and are therefore not shown in the sectional view.

The product to be fluidized and thermally treated, which is in particular polyethylene terephthalate (PET), is introduced into the device 1 from above via a product inlet 7 and leaves the device 1 via a product outlet 8. Fluidizing gas is introduced via a gas inlet 9 blown into the device 1 below the sieve tray 11 and, after it has passed through the zigzag separator 12, is drawn off via a gas outlet 10 in the ceiling area of the device 1. The granulate entering the device 1 first reaches the first chamber 2, which takes up a large part of the total chamber volume, and is fluidized by the fluidizing gas entering via the sieve tray 11, whereby a fluidized bed 23 of granules and fluidizing gas is formed. The fluidized bed behaves like a fluid, i.e. a gravitational pressure forms within the fluidized bed, and the fluidized bed flows through the product passages 18, 19, 20 and 21 between a lower end region of the partition walls 14, 15, 16 and 17 respectively and the sieve plate 11 from the first chamber 2 into the adjoining chambers 3, 4, 5 and 6. At the end of the last chamber 6 there is a window 22 in the end wall at a certain height above the sieve plate 11 and defines this height the height of all fluidized beds 23 in all chambers 2, 3, 4, 5 and 6. The fluidized bed 23 is shown schematically in FIG.

Bubbles can form within the fluidized bed 23, which rise upward within the fluidized bed and can combine to form larger bubbles 24, which burst as soon as they reach the fluidized bed surface 26 and can hurl the granules around within the chamber. This is shown schematically in the area of reference number 25.

2 shows a vertical sectional view of a second exemplary embodiment of the device 1 according to the invention. The second exemplary embodiment differs from the first exemplary embodiment in that in the successive partition walls 14, 15, 16 and 17 between the chambers 2, 3, 4, 5 and 6, the product passages 28, 29, 30 and 31 are arranged alternately at a certain height above the sieve plate 11 in the partitions 14 and 15 and directly on the sieve plate 11 in the partitions 15 and 17. As a result, the granulate particles are transported on their way through the chambers 2, 3, 4, 5 and 6 in an alternating way running up and down, similar to a roller coaster. This has the advantage that the upstream product passage and the downstream product passage are as far apart as possible in each chamber. As a result, all of the granulate particles are forced as long as possible through each of the chambers 3, 4, 5 and 6, which at least ensures that as few granule particles as possible have a short residence time.

This is particularly advantageous in the crystallization of polyesters, since their stickiness is largely overcome after a minimum residence time in a crystallizer, while excessively long residence times do not impair the product quality. Due to the cascade-like arrangement of the product passages 28 and 30, the volume of the fluidized beds from the first chamber 2 via the second and third chamber 3, 4 to the fourth and fifth chamber 5, 6 is getting smaller and smaller. All in Fig. 1 and Fig. 2 identical reference numerals refer to the same or corresponding elements of the device 1.

3a shows a vertical sectional view of a third exemplary embodiment of the device 1 according to the invention, while FIG. 3b shows a horizontal sectional view of this third exemplary embodiment. As can best be seen in FIG. 3b, the device 1 consists of a centrally arranged cylindrical chamber 2, which in turn takes up a large part of the entire chamber volume of the device 1, and of peripheral chambers 3, 4, 5 and 6, which are separate connect radially to the central chamber 2 and surround it along its entire circumference. The central chamber 2 is separated by a partition 14 from the radially surrounding chambers 3, 4, 5 and 6, which in turn are limited to the outside by the housing wall 13. Between the chambers 3, 4, 5 and 6 there is a partition 15, 16 and 17, respectively, so that again four equal chambers 3, 4, 5 and 6 are formed. At a certain height above the sieve bottom (FIG. 3a) there is a product passage 18 which forms the connection between the first chamber 2 and the second chamber 3. The product passages between the chambers 3, 4, 5 and 6 are not shown. However, they correspond to the product passages 18, 19, 20 and 21 of FIG. 1 and the product passages 28, 29, 30 and 31 of FIG. 2.

The height and / or cross-sectional dimension of the window 22 can be adjustable both in FIG. 1 and in FIG. 2 and in FIG. 3b. The height of the fluidized bed 23 is determined by the adjustability of the height, while the throughput through the device 1 can be adjusted by the adjustability of the cross-sectional dimension. Both in the exemplary embodiments 1 and 2 with a rectangular geometry and in the exemplary embodiment 3 with a cylindrical geometry, the product passages can only be arranged on the floor (see product passages 18, 19, 20 and 21 in FIG. 1), or they can alternate at the top and be arranged below, which creates a roller coaster arrangement (see product passages 28, 29, 30 and 31 in Fig. 2), or they can alternately on the left or right end area of the successive partitions 14, 15, 16 and 17 in the area of Sidewall may be arranged so that a slalom arrangement (not shown) is formed. Three different exemplary embodiments of the device 1 according to the invention have been described in FIGS. 1, 2 and 3a and 3b described above. In all three cases, there are different construction variants of a 5-stage fluidized bed 23. They differ in the arrangement of the chambers 2, 3, 4, 5, 6 and the product passages 18, 19, 20, 21; 28, 29, 30, 31 and the product openings 22. The 5-stage fluidized bed 23 each consists of a large chamber 2, the (main) crystallization chamber, and four subsequent smaller chambers 3, 4, 5, 6 of the same size, which for are responsible for the homogenization of the product. The chambers 3, 4, 5, 6 are either strung together or arranged concentrically around the larger chamber 2. The fluidized bed apparatuses 1 are fed by a single gas supply. Due to the pressure drop across the sieve plate 11 and the fluidized bed 23, the gas is distributed over the individual chambers 2, 3, 4, 5, 6. The product passages 18, 19, 20, 21; 28, 29, 30, 31 are arranged below, above or alternately below / above. In the exemplary embodiment of FIG. 1, a fluidized bed 23 of uniform height is established in the chambers 2, 3, 4, 5, 6 due to the product passages 18, 19, 20, 21 located below. This can be regulated by the height of the product outlet window 22 in the last chamber 6. In the embodiment of FIG. 2, the layer height of the fluidized bed 23 in the chamber 2, the chambers 3 and 4 and the chambers 5 and 6 can be adjusted independently of one another due to the product passages 28, 29, 30, 31 alternating at the top and bottom by the height position of the overhead product passages 28, 30 is set.

4 shows the dimensionless residence time spectrum n of ideally mixed fluidized chambers or stirred tanks connected in series (stirred tank cascade). As a basis for the calculation, it was assumed that the mean dwell time of the product in the individual vortex chambers or stirred tanks is the same. It can be seen that with an increasing number of vortex chambers or stirred tanks, the residence time spectrum becomes narrower and thus the thermally treated product becomes more homogeneous at the outlet of the apparatus. With an infinite number of vortex chambers or stirred tanks, a pure plug flow is obtained. Then all particles are exposed to the effects that take place in the individual chambers or boilers for the same length of time, and a product of very uniform quality is obtained. In practice, it is often sufficient to put the device in to divide a few chambers in order to achieve an improved and sufficiently high quality of the product.

5a and 5b schematically show a one-stage and a 5-stage fluidized bed. 5c shows as a result of a calculation example the local course of the product temperature of both this single-stage and this 5-stage fluidized bed. In the example, the local product temperature profile (temperature distribution) of the 5-stage fluidized bed was compared with the local product temperature profile (temperature distribution) of the single-stage fluidized bed. The product throughput and the operating parameters represent the industrial plants built today. It must be noted at this point that the heat of crystallization released was taken into account in the heat balance of the first chamber (a large part of the exothermic crystallization reaction also takes place here). It can be seen that by dividing the fluidized bed into several stages / chambers, the efficiency of the heat exchange between gas and granules could be significantly improved, while improving the quality and homogeneity of the end product. The thermal efficiency (defined and measured as the ratio [product temperature at the product outlet - product temperature at the product inlet] / [treatment gas temperature at the gas inlet - product temperature at the product inlet]) was increased by around 7.5% for this example. Due to the higher product temperature after crystallization, a subsequent process step for solid-phase post-condensation (SSP) can be saved on the apparatus size required there.

Conclusion: The multi-stage fluidized bed of the present invention is characterized both by an improved, i.e. narrower residence time spectrum of the product in this multi-stage fluidized bed as well as an improved, i.e. increased thermal efficiency of the thermal treatment of the product.

6a and 6b show a particularly advantageous first embodiment of the product passages between the chambers of the device according to the invention.

FIG. 6a corresponds to a detail from FIG. 1, which shows the partition walls 14, 15, 16 and 17 in their lower region in the vicinity of the sieve plate 11. The sieve bottom 11 has Holes 11a formed by punching out material and removing material. In contrast to Fig. 1, however, the lower end of the partitions 14, 15, 16 and 17 is provided with a guide plate 33, 34, 35 and 36 in this embodiment, which is on both sides of the respective partition and perpendicular to it into the chambers extends on both sides of the respective partition. By the guide plates 33, 34, 35, 36 a back mixing, ie a backward movement of granulate particles against the granulate flow is made more difficult. Backmixing reduces the thermal efficiency and leads to a broadening of the residence time spectrum on the side of the longer residence times. As a result of the tunnel-like product passages 18, 19, 20, 21 thus formed, it is unlikely that a granulate particle will move from a chamber back to a chamber upstream from this chamber in the opposite direction to the flow of the fluidized granulate, since it will travel between the sieve plate 11 and the respective guide plate 33, 34, 35, 36 is in all likelihood reflected back and forth and has to be in this tunnel for a while, so that ultimately it is most likely to be carried along by the granulate particles drifting in the direction of flow of the granulate.

FIG. 6b shows a second embodiment of the product passages 18, 19, 20, 21 which is improved compared to the first embodiment of FIG. 6a. The section of FIG. 6b corresponds to the section of the first embodiment of the product passages circled in FIG. 6a with the difference that here in the area of the tunnel opposite the respective guide plate 33, 34, 35, 36, the sieve plate 11 has holes 11b, which were formed by only partially punching out material and bending this partially punched out material. Through these holes 11b, in addition to their vertical fluidization component perpendicular to the direction of flow of the granulate, a movement component parallel to and in the same direction as the direction of flow of the granulate is impressed on the blown-in air. This makes backmixing even less likely than in the embodiment of FIG. 6a.

Conclusion: Thus, the two designs of the product passages 18, 19, 20, 21 of FIGS. 6a and 6b contribute to a further improvement in the thermal efficiency and narrowing of the residence time spectrum of the device 1 according to the invention. LIST OF REFERENCE NUMBERS

contraption

chamber

product entry

product outlet

gas inlet

gas outlet

Sieve plate a punched holes with removed material b partially punched holes with bent material

Zigzag separator

casing

partition wall

Product passage

fluidized bed

Bubble bursting bubble

Fluidized bed surface 44

18

Product passage

baffle

Claims

claims

1. Device (1) for the continuous thermal treatment of granular bulk goods (granules), in particular for crystallizing polymer granules, such as e.g. Polyethylene terephthalate (PET), having a product inlet (7) which opens into a first most upstream chamber (2) and a product outlet (8) which adjoins a most downstream chamber (6), characterized in that that the device (1) has a plurality of adjoining fluidization chambers (2, 3, 4, 5, 6), each with a sieve plate (11), through which the respective chamber (2, 3, 4, 5, 6) comes from below A fluidizing gas for fluidizing the granules can be blown in via a gas inlet (9) and can escape via a gas outlet (10) in the ceiling area of the device (1), the first chamber (2) making up a large part of the total volume of all chambers (2, 3 , 4, 5, 6), and that adjacent chambers each have a fluid connection via product passages (18, 19, 20, 21; 28, 29, 30, 31) in the partition walls (14, 15, 16, 17) arranged between them - have dung.

2. Device according to claim 1, characterized in that product passages (18, 19, 20, 21) between adjacent chambers on the bottom side between the sieve bottom (11) and a lower end region of the partition (14, 15, 16, 17) between the adjacent chambers (2, 3, 4, 5, 6) are arranged.

3. Device according to claim 1 or 2, characterized in that product passages between adjacent chambers on the wall side between a side wall and a lateral end region of the partition (14, 15, 16, 17) between the adjacent chambers (2, 3, 4, 5, 6 ) are arranged.

4. Device according to one of claims 1 to 3, characterized in that product passages (28, 30) in the partition (14, 16) are arranged approximately at the level of the upper end of the fluidized bed.

5. Device according to one of claims 1 to 4, characterized in that the product passages (18, 19, 20, 21; 28, 29, 30, 31) over the entire width or over the entire height of the device (1) extend from one side wall to the other side wall or from the sieve bottom (11) to the upper end of the fluidized bed (26).

6. Device according to one of claims 2 to 5, characterized in that the product passages (18, 19, 20, 21; 28, 29, 30, 31) are slit-like.

7. The device according to claim 6, characterized in that the slit-like product passages (18, 19, 20, 21; 28, 29, 30, 31) each along the entire width or along the entire height of a partition (14, 15, 16, 17) extend.

8. Device according to one of the preceding claims, characterized in that the product passages (28, 29, 30, 31) alternately on the sieve plate (11) and at the height of the on the product conveying direction along the partition walls (14, 15, 16, 17) upper fluidized bed end (26) are arranged.

9. Device according to one of claims 1 to 7, characterized in that the product passages are arranged alternately on the left wall-side end and on the right wall-side end of the partition on successive along the product conveying direction partition walls (14, 15, 16, 17).

10. Device according to one of the preceding claims, characterized in that the position of the product passages (28, 30) is adjustable.

11. Device according to one of the preceding claims, characterized in that the cross-sectional extent of the product passages (18, 19, 20, 21; 28, 29, 30, 31) is adjustable.

12. Device according to one of claims 8 to 11, characterized in that a minimum dimension, in particular the slot width of the cross-sectional dimension of the product passages (18, 19, 20, 21; 28, 29, 30, 31) in the range between a minimum granule dimension and is about 20 cm.

13. The apparatus according to claim 12, characterized in that the minimum dimension, in particular the slot width of the cross-sectional dimension of the product passages (18, 19, 20, 21; 28, 29, 30, 31) in the range between 2 times a minimum granule dimension and is about 10 times the minimum granule size.

14. Device according to one of the preceding claims, characterized in that the bottom or the approximately at the level of the upper fluidized bed end (26) in the partition or the wall-side product passages (18, 19, 20, 21) each one to the sieve bottom (11) or to the respective side wall essentially parallel and to the partition (14, 15, 16, 17) essentially vertically arranged baffle (33, 34, 35, 36), which at the edge of the respective product passage (18, 19, 20, 21) is fixed and extends through the product passage on both sides of this partition (14, 15, 16, 17) into the two adjacent chambers.

15. The device according to claim 14, characterized in that in the region of the bottom product passages substantially opposite from the guide plate (33, 34, 35, 36) are arranged blowing areas in the sieve bottom (11) which blow fluidizing gas into the chamber (2 , 3, 4, 5, 6) with a speed that enables both a speed component perpendicular to the blowing area and a speed component parallel to the blowing area in the direction of the fluidized granulate flow.

16. Device according to one of the preceding claims, characterized in that at least the first chamber (2) is connected via its sieve plate (11) to an associated feed channel for fluidizing gas, which is provided by a common feed channel for the remaining chambers (3, 4, 5, 6) is separated.

17. Device according to one of claims 1 to 15, characterized in that all chambers (2, 3, 4, 5, 6) are assigned to a common feed channel for fluidizing gas via their respective sieve plate (11).

18. Device according to one of the preceding claims, characterized in that it has an impact resolver at the product outlet (8) into which the product outlet opens.

19. Device according to one of the preceding claims, characterized in that the sieve trays (11) of all chambers (2, 3, 4, 5, 6) are arranged in one plane.

20. Device according to one of claims 1 to 18, characterized in that the sieve trays of the chambers lined up along the fluidized granulate stream are arranged at mutually offset heights.

21. Device according to one of the preceding claims, characterized in that the first chamber (2) is defined in its floor plan by a wall (14) which surrounds it cylindrically and the remaining chambers (3, 4, 5, 6) are around the first Connect chamber (2) concentrically radially outwards with cylindrical walls.

22. The device according to any one of claims 1 to 20, characterized in that the first chamber is defined by a pair of concentric cylindrical walls in its plan, the remaining chambers within the inner Connect the cylindrical wall of the first chamber concentrically radially inwards with cylindrical walls.

23. Device according to one of claims 1 to 20, characterized in that the first chamber is rectangular in plan and the remaining chambers adjoin the first chamber to the outside.

24. The device according to any one of claims 1 to 20, characterized in that the first chamber is rectangular in its plan and the remaining chambers within the first chamber are nested inside each other concentrically with each also rectangular plan.

25. Device according to one of the preceding claims, characterized in that the remaining chambers are each designed such that in them the ratio between the layer height of the fluidized granules and the smallest floor plan chamber dimension is in the range from 0.5 to 2.

26. Device according to one of the preceding claims, characterized in that the most upstream first chamber (2) takes up a large part of the total volume of all chambers (2, 3, 4, 5, 6).

27. The device according to claim 26, characterized in that the volume of the first chamber (2) is approximately half of the total volume of all chambers (2, 3, 4, 5, 6).

28. Device according to one of the preceding claims, characterized in that the sieve bottom surface of the first chamber (2) takes up a large part of the entire sieve bottom surface.

29. The device according to claim 28, characterized in that the sieve bottom surface of the first chamber (2) is approximately half of the total sieve bottom surface of all chambers (2, 3, 4, 5, 6).

30. Device according to one of the preceding claims, characterized in that a zigzag separator (12) is arranged in the ceiling area of the device (1) between the fluidized bed surface (26) and the fluidizing gas discharge.

31. Device according to one of the preceding claims, characterized in that at the downstream end of the last chamber (6) the product outlet in a wall is window-like (22) and a slide is provided through which the lower edge of the window (22) adjusts can be.

32. Device according to one of claims 1 to 30, characterized in that at the downstream end of the last chamber (6) the product outlet is designed as a kind of pivotable weir, the height of which can be adjusted by pivoting the weir.

33. Process for the continuous thermal treatment of a granular bulk material (granules), in particular for crystallizing polymer granules, such as e.g. Polyethylene terephthalate (PET), using the device according to one of claims 1 to 27, characterized in that the granules are passed through the several fluidization chambers arranged in series, each of which has a sieve plate, through which a fluidizing gas for fluidizing into the respective chamber from below of the granules is blown in and pulled off in the ceiling area of the device, the absolute filling level of the fluidized granules in the first chamber being at least as high as the absolute filling level of the remaining chambers downstream.

34. The method according to claim 33, characterized in that fluidizing gas is blown into all chambers with a uniform first treatment temperature.

35. The method according to claim 34, characterized in that the fluidizing gas is used as a heat source for heating the fluidized granules.

36. The method according to claim 33 to 35, characterized in that the fluidizing gas at least partially contains a gas reacting with the fluidized granules.

37. The method according to claim 33 to 36, characterized in that a fluidizing gas with a second treatment temperature is blown into at least one of the remaining chambers.

38. The method according to claim 37, characterized in that the fluidizing gas is used as a heat sink for cooling the fluidized granules.

39. The method according to claim 33 to 38, characterized in that fluidizing gas is blown into all chambers with the same overpressure and the same gas velocity.

40. The method according to claim 33 to 38, characterized in that fluidizing gas is blown into the first chamber with a higher pressure and / or higher gas velocity than in the remaining chambers.